Abstract
The purpose of this study was to determine the incidence of the three types of acromial morphology with respect to age.
A total of 448 anteroposterior (AP) radiographs were obtained from 224 healthy subjects. According to Bigliani's classification, acromial morphology was classified in three types; Type I (flat), Type II (curved), Type III (hooked). We evaluated acromial type in three age groups; Group 1: 25–35 years (67 cases); Group 2: 36–55 years (100 cases); Group 3: 56–65 years (57 cases).
We found a significant difference in the distribution of acromion types between Group 1 and Group 3 (p = 0.04), and on the left shoulder (p = 0.03). Type I acromion was more prevalent on left shoulder in Group 1. Type III was more prevalent in both shoulders in Group 3.
Our study raised the possibility that different shapes of acromion may be acquired as a response to traction forces applied via the coracoacromial ligament, and excessive use of an upper extremity may be responsible for these secondary acromial changes. However, we also considered that Type III acromion may be congenital, but it is a rare anatomic variation in healthy young population.